1. Field of the Invention
The present invention relates to the manufacture of fiberglass insulation materials, and more particularly to the preparation of phenolic resin for glass fibers.
2. Brief Description of the Prior Art
Aqueous dispersions of phenol-formaldehyde resole resins are frequently used in the manufacture of glass fiber insulation materials, such as insulative batts for walls, in roofs and ceilings, insulative coverings for pipes, and the like. Typically, after glass fiber has been formed, the still hot fiber is sprayed with aqueous binder dispersion in a forming chamber or hood, with the fibers being collected on a conveyer belt in the form of a wool-like mass associated with the binder. In some cases, a glass fiber web is sprayed with the aqueous dispersion. Both resole and urea-modified resole resins have been employed for this purpose, the urea contributing to the xe2x80x9cpunkingxe2x80x9d resistance of the binder (i.e., resistance to exothermic decomposition at elevated temperatures), and reducing volatiles liberated when the resin is cured at elevated temperature.
An excess of formaldehyde over phenol is typically used so as to minimize the free phenol in the reaction product. Subsequently, other components (for example, urea) may be included to scavenge free formaldehyde.
Frequently, in the manufacture of glass fiber insulation materials, the aqueous resole resin is prepared in advance of the preparation of the binder, or is supplied by a resin manufacturer and stored until shortly before use. The resole is typically prepared by reaction of phenol and formaldehyde under basic conditions, the resulting reaction mixture being neutralized to a slightly basic pH by addition of a strong acid, to provide a water-dilutable resole. Subsequently, the binder is prepared by adding to the resole resin an acid catalyst for curing the resin, water to dilute the dispersion, and optionally other components, such as a silane glass-adhesion promoter, an oil emulsion lubricant, and urea to reduce volatile materials liberated during curing.
It is desirable to obtain the highest possible level of solids during preparation of the resole resin. High solids correlate with reduced volatile liberation and enhanced efficiency.
The resole resin can be prepared by any of a variety of specific processes, such as disclosed in U.S. Pat. No. 5,300,562, hereby incorporated by reference. Often, a single stage process is employed. Phenol and formaldehyde are mixed with a strongly basic catalyst, such as an alkali metal base, and the mixture is maintained at an elevated temperature until the desired degree of reaction has occurred, after which time the reaction mixture is cooled and neutralized by addition of a suitable acid. Alternatively, a multiple step process can be employed such one involving an initial reaction step under acid conditions and a subsequent reaction step under basic conditions, followed by neutralization.
U.S. Pat. No. 5,362,842 discloses a two-step process for making a urea-formaldehyde resin composition including an initial step under basic conditions and a second step under acidic conditions, during which the pH is maintained in the range from 4.9 to 5.2.
U.S. Pat. Nos. 5,358,748 and 5,505,998 disclose an acidic glass fiber binding composition. A strong aqueous soluble acid is employed in preparing the binder composition in order to reduce the level of alkylamine otherwise produced during cure. Alklyamines are disclosed to be undesirable odiferous materials produced by degradation of urea (the formaldehyde scavenger) during cure. A strong acid, that is, an acid with a pKa value of 4 or less, is added to the binder composition to lower the pH to a value between 4.5 and 6.5, preferably between 4.5 and 6. Suitable acids include sulfamic acid, oxalic acid and sulfuric acid. The binder includes a phenol formaldehyde resin, preferably having a low free formaldehyde content and a low free phenol content. According to this patent, most commercially available phenol formaldehyde resins have an alkaline pH range, such as between 9 and 9.6, and this makes the addition of the strong acid to provide a pH between 4.5 and 6.5 a quite different thing.
According to U.S. Pat. No. 5,538,761, phenol-formaldehyde condensates prepared under acid conditions or with low levels of formaldehyde under basic conditions are generally not water soluble, as significant quantities of insoluble dihydroxydiphenylmethanes are produced.
U.S. Pat. No. 5,538,761 discloses a process for preparing binder-treated fiberglass exhibiting lower formaldehyde and ammonia emissions by use of an acidifying hydrolyzable salt, a mineral acid, or partial ester of carboxylic acid to lower the instantaneous pH of the urea-extended pre-react binder solution to less than 5.5, and preferably in the range 3.0 to 5.0, and more preferably in the range 4.0 to 5.0. The process also includes coating fiberglass with the acidified solution, and curing the binder. The xe2x80x9cpre-reactxe2x80x9d is a binder solution comprising phenol-formaldehyde resole resin to which urea has been added and permitted to react with the free formaldehyde.
U.S. Pat. No. 5,864,003 discloses a thermosetting resin composition containing a mixture of a phenol-formaldehyde resole resin and a latent curing agent. The latent curing agent acts synergistically with a strong acid catalyst of the type conventionally used to cure phenol resole resins. Such strong acid catalysts include inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid and organic acids such as sulfamic acid, tricholoracetic acid, and aromatic di- and polysulfonic acids, such as phenyl sulfonic and other organosulfonic acids. The U.S. Pat. No. 5,864,003 patent notes that the resole resin can be neutralized after alkaline reaction of the phenol and formaldehyde using a conventional acid neutralizing agent such as methane sulfonic acid, hydrochloric acid, phosphoric acid, or sulfuric acid. Neutralization is accomplished by adding a sufficient amount of acid to establish a pH of between 6.5 and 7.5 in the aqueous resin, although a pH as low as 4.0 may result in stable resin systems.
Given the large volume of resinous binder compositions required in the production of fiberglass insulation and for other uses, and the need to minimize offensive emissions of formaldehyde and other compounds during manufacture, there is a continuing need for phenol-formaldehyde resin compositions for use in binders which exhibit low emissions during cure, and that have high solids.
The present invention provides an improved method or process for preparing a phenolic resin for use as a binder for glass fibers and giving higher solids than prior art processes. Higher solid compositions are very desirable from an emission-reduction perspective. This process provides more efficient resin compositions by increasing the solids level of the resin composition, and reduced emissions during cure, while maintaining good storage stability, as determined by the water dilutability of the resin composition, and exhibiting good curing characteristics. The process can be used to prepare compositions including either water-soluble phenol-formaldehyde resole resins or water-soluble phenol-formaldehyde resole resins modified with a nitrogenous reactant such as urea and/or ammonia. In the case of urea-modified phenol-formaldehyde resins, the present invention provides unexpected improvement in binder cure profiles. The present process provides compositions that exhibit very good stability, even at low pH.
The process comprises preparing a water-soluble phenol-formaldehyde resole resin by first preparing an initial aqueous mixture including formaldehyde and phenol, and adding a basic polymerization catalyst to the initial aqueous mixture. The aqueous mixture is then maintained at a predetermined temperature during reaction of the phenol and formaldehyde to form the water-soluble phenol-formaldehyde resole resin until the free formaldehyde content of the aqueous mixture drops to a predefined level. Next, the aqueous mixture is cooled, and finally acidified to a pH of no greater than 3. Preferably, the aqueous mixture including the unmodified resole resin is acidified to a pH from about 2 to 3.
The acidified resole resin of the present process is stable at low pH. The acidified resole resin can be modified by subsequent addition of one or more acidic modifiers to alter or improve the properties of the resulting resin and/or the binder subsequently prepared from the resole resin. Examples of suitable acidic modifiers that can be employed include latent catalysts such as ammonium sulfate, reactive diluents such as benzylic alcohols, weak acids such as boric acid, and fatty acids such as oleic and stearic acids, polycarboxylic acids such as polyacrylic acids, and esters, such as diethyl phosphite.
Optionally, the process can be used to prepare a modified phenol-formaldehyde resin composition by preparing an aqueous reaction mixture including the phenol-formaldehyde resole resin and a nitrogenous reactant, such as urea, ammonia, or a mixture of urea and ammonia; and permitting the nitrogenous reactant to react with the phenol-formaldehyde resole resin to form a modified resin.
Subsequently, preparation of the binder is completed by adding a catalyst for curing the resole resin.
Preferably, the phenol-formaldehyde resin has a formaldehyde-to-phenol mole ratio of from about 2.5:1 to 4.2:1, and more preferably, from about 3.2:1 to 4.0:1. It is also preferred that the predefined level be about 40 percent by weight of the free formaldehyde in the initial aqueous mixture.
Further, the process of the present invention also optionally provides for adding ammonia and/or urea to the reaction mixture as a formaldehyde scavenger. Preferably, the ammonia is added in sufficient quantity to give a weight ratio of formaldehyde scavenger to solids of unmodified resin of from about 1.0:100 to 3.0:100.
When a urea or ammonia-modified binder is desired, it is preferred that the mole ratio of the urea or ammonia modifying agent to the free formaldehyde of the phenol-formaldehyde resin be from about 1:1 to 1.75:1, and that the aqueous mixture be maintained at a temperature of from about 5xc2x0 C. to 30xc2x0 C. while permitting the modifying agent to react with the resole resin.
The present invention also provides a process for producing a glass fiber batt, which comprises preparing a binder as described above and spraying the binder on glass fibers to form a batt; and then curing the binder at an elevated temperature.
In completing preparation of the aqueous mineral fiber binder composition, other typical binder components, such as an acid elevated temperature cure catalyst, a mineral oil lubricant, and an organo-silane adhesion promoter, can be added to the aqueous mixture of the modified resole. Such components can be added to the aqueous mixture of modified resole resin shortly before application of the binder to the glass fibers.